Ultraviolet (UV) irradiation from the sun is a well-recognized, otent environmental insult, and skin is directly exposed to UV irradiation. Long-term exposure to UV irradiation damages human skin connective tissue and promotes formation of skin cancer, the most common form of human cancer. Connective tissue abnormalities in sun-exposed skin largely result from reduced synthesis and elevated degradation of type I collagen, the most abundant structural protein in skin. Most skin cancer occurs in nearly all adult individuals and is therefore a significant public health concern. In photodamaged skin, damaged connective tissue impairs the structural integrity and functions of the skin, and creates a tissue environment of skin cancer and delayed wound healing. Solar UV irradiation generates reactive oxygen species (ROS), which mediate many of the harmful effects on sun exposure on skin. We find that Cystein-rich protein 61 (CYR61), a secreted, extracellular matrix-associated protein, is markedly elevated by oxidative stress, and involved in oxidative stress-mediated aberrant collagen homeostasis in human skin dermal fibroblasts. CYR61 is substantially elevated in the dermis of chronically sun-exposed skin, and acutely UV-irradiated human skin in vivo. Elevated CYR61 exerts dual effects on collagen homeostasis by inhibiting type I collagen production and promoting collagen degradation, thereby causing a net deficit of dermal collagen in human skin. Moreover, we find that CYR61 is required for UV irradiation-induced down-regulation of type I collagen and up-regulation of MMP-1 in human skin fibroblasts. Importantly, reducing ROS levels by antioxidant treatment substantially suppresses elevated CYR61, and thereby protects against aberrant collagen homeostasis caused by oxidative stress in human skin dermal fibroblasts. Based on our new preliminary data, we hypothesize that elevated CYR61 is regulated by oxidative stress, and that reducing CYR61 by antioxidant prevents UV/oxidative stress-induced aberrant collagen homeostasis in UV-irradiated and chronically sun-exposed human skin in vivo. To test the above hypothesis, we propose the following Specific Aims. Aim 1: Determine the ability of antioxidant to reduce UV irradiation-induced CYR61 expression and aberrant collagen homeostasis in human skin in vivo. Aim 2: Determine molecular mechanisms by which oxidative stress regulates CYR61 in human skin dermal fibroblasts. This revision proposal is a natural extension of the parent grant, and offers unique opportunities to investigate molecular mechanisms by which oxidative stress regulates CYR61, in human skin in vivo. PUBLIC HEALTH RELEVANCE: The long-term, broad goal of the proposed research is to understand he molecular basis of oxidative stress-mediated skin connective tissue damage, which is caused by exposure to solar ultraviolet (UV) irradiation. Damage to skin connective tissue by UV/oxidative stress impairs the structural integrity and functions of the skin, and creates a tissue environment that promotes skin cancer, the most common form of human cancer. As such, the deleterious impact of solar UV/oxidative stress on skin represents a significant public health concern.